The increased use of electrical/electronic devices in automotive vehicles has been accompanied by the expanded application of secondary batteries, electrolytic capacitors, capacitors, and other chargeable storage batteries.
JP-A-2003-308810 illustrates a structure of a storage battery in which an accumulator element is housed in a sealed case. This storage battery will be described with reference to FIG. 12 hereof.
The storage battery 100 shown in FIG. 12 comprises a cylindrical case 101; an accumulator element 102 housed in the cylindrical case 101; lead wires 103 extending from the accumulator element 102; collector plates 104, 104 connected to a positive or negative pole of the lead wires 103; end plates 108, 108 for closing openings at either end of the cylindrical case 101; electrode rods 105, 105 that extend from the collector plates 104, 104 and pass through the end plates 108, 108; nuts 106, 106 threaded onto distal ends of the electrode rods 105, 105; and pins 107, 107 passing through the collector plates 104, 104 from the end plates 108, 108 toward the center of the cylindrical case 101.
A DC voltage is applied to the electrode rods 105, 105 through harnesses 109, 109, enabling electrical energy to be stored in the accumulator element 102. The electrical energy stored in the accumulator element 102 can also be drawn out via the electrode rods 105, 105, and the harnesses 109, 109.
The harnesses 109, 109 are fixed to the electrode rods 105, 105 by the nuts 106, 106. A rotational force is applied to the electrode rods 105, 105 when the nuts 106, 106 are threaded on, but rotation of the collector plates 104, 104 is restricted by the pins 107, 107. Therefore the electrode rods 105, 105 do not rotate.
The pins 107, 107 play a vital role in preventing rotation of the collector plates 104, 104 and the electrode rods 105, 105.
If L1 is taken as the length of the accumulator element 102 and L2 is taken as the length of the cylindrical case 101, then the length L2 of the cylindrical case will determine the length of the pins 107, 107, and will therefore increase. Specifically, the length L1 of the accumulator element 102 is determined by the desired storage capacity. The length L2 of the cylindrical case 101 increases in relation to the length L1, and a problem is presented insofar as the case 101 increases in size proportionately in regard to the storage capacity.
Furthermore, the storage battery 100 is filled with an electrolyte to bring about an electrochemical reaction. A part of the electrolyte is converted to a gas by the electrochemical reaction. The internal pressure of the storage battery 100 increases due to the resulting gas. The cylindrical case 101 is a tube and is therefore highly capable of resisting the internal pressure, but the end plates 108, 108 are flat plates and are therefore not highly capable of withstanding the internal pressure.
In order to compensate for this weakness, the end plates 108, 108 are made several times as thick as the cylindrical case 101. The weight of the storage battery 100 increases due to the additional thickness of the end plates 108, 108.
When multiple storage batteries are to be mounted in a vehicle, the storage battery 100 is preferably made smaller and lighter.